Synthesis of lifepo4 under hydrothermal conditions

ABSTRACT

The present invention relates to a process for the preparation of compounds of general Formula (I) L a−b M 1   b Fe 1−c M 2   c P d−e M 3   e O x  (I), wherein Fe has the oxidation state +2 and M 1 , M 2 , M 3 , a, b, c, d, e and x are: M 1 : Na, K, Rb and/or Cs, M 2 : Mn, Mg, Al Ca, Ti Co, Ni, Cr, V, M 3 : Si, S, F a: 0.8-1.9, b: 0-0.3, c: 0-0.9, 15 d: 0.8-1.9, e: 0-0.5, x: 1.0-8, depending on the amount and oxidation state of Li, M 1 , M 2 , P, M 3 , wherein compounds of general Formula (I) are neutrally charged, comprising the following steps (A) providing a mixture comprising at least one lithium-comprising compound, at least one iron-comprising compound, in which iron has the oxidation state +3, and at least one M 1 -comprising compound, if present, and/or at least one M 2 -comprising compound, if present, and/or least one M 3 -comprising compound, if present, and at least one reducing agent which is oxidized to at least one compound comprising at least one phosphorous atom in oxidation state +5, and (B) heating the mixture obtained in step (A) at a temperature of 100 to 500° C. and at an autogeneous pressure to reduce Fe to oxidation state +2 and to obtain a compound of general Formula (I).

The present invention relates to a process for the preparation ofcompounds comprising lithium, iron and phosphate-anions, to a processfor the preparation of mixtures comprising these compounds and at leastone electrically conducting material, to the compounds and the mixtures,preparable by these processes and the use of these compounds andmixtures for the preparation of cathodes of lithium ion batteries.

Processes for the preparation of LiFePO₄ are already known from theprior art.

US 2003/0082454 A1 discloses a method for preparing LiFePO₄ by mixingLi₂CO₃ or LiOH H₂O, Fe(CH₃CO₂)₂ and NH₄H₂PO₄ H₂O. The solid mixture iscalcinated at 300 to 350° C., in order to eliminate NH₃, H₂O and CO₂.The mixture is subsequently further processed under argon for 24 hoursat 800° C. This document further mentions the method of preparingLiFePO₄ based material by calcination of a milled mixture comprisingLi₂C₂O₄, LiH₂PO₄ and Fe(C₂O₄)·2H₂O.

U.S. Pat. No. 6,702,961 B2 also discloses a method for the preparationof LiFePO₄ by pelletising a milled mixture consisting of FePO₄, Li₂CO₃and carbon, followed by calcination at 700° C. for 8 hours in an inertatmosphere.

The abstract of CN 1547273 A discloses a method for the preparation ofLiFePO₄ by calcination of a milled and subsequently tablettized mixtureof Li₂CO₃, FeC₂O₄·2H₂O and (NH₄)₂HPO₄ with the addition of carbon undermicrowave radiation.

DE 10 2005 015613 A1 and DE 10 2005 012 640 A1 disclose that LiFePO₄ canbe obtained by hydrothermal treatment of an aqueous mixture comprisingFe(II)SO₄·7H₂O, H₃PO₄ and LiOH H₂O under nitrogen at 160° C. for 10hours. During said hydrothermal treatment the desired LiFePO₄precipitates from the aqueous mixture. No component of the reactionmixture is reduced or oxidized.

WO 2006/057146 A2 discloses that LiFePO₄ can be obtained by melting amixture comprising Fe(II)O, P₂O₅ and LiOH at 1100° C. under argon,followed by milling.

The processes for the preparation of LiFePO₄ according to the prior artbear the drawback that an additional reducing agent like carbon has tobe added to the reaction mixture or that the calcination step has to beconducted in a reducing atmosphere. Because the added carbon acts as areducing agent only at high reaction temperatures, high calcinationtemperatures are necessary which lead to a material with large crystalgrains and with a broad particle size distribution.

Other disadvantages are that if solid compounds like Li₂CO₃ and Fe₂O₃are mixed in solid phase, it is difficult to obtain a mixture having ahomogenous dispersion of the different ions throughout the wholemixture. In addition, carbon containing reducing agents show thedisadvantage that their reducing power is not independent from theamount in which they are used, and therefore it is not easy to foreseewhich amount of carbon containing reducing agent is needed for thereduction and which amount can be used as electrically conductingmaterial.

The object of the present invention is to provide a process for thepreparation of lithium-iron-phosphate which makes it possible to obtainthese compounds in a very homogenously mixed and crystalline state. Inaddition, it is an object of the present invention to provide a processfor the preparation of the mentioned compounds which can be conductedeasily and in only two reaction steps. Moreover, it is a preferredobject of the present invention to provide a process for the preparationof lithium-iron-phosphate, in which no calcination step is necessary atall. It is another object to provide a process in which only the desiredcompound is obtained without any disturbing side products making anypurification and/or washing steps unnecessary. It is a further object toobtain a more finely dispersed material with a very narrow sizedistribution of the crystallites, supplying improved Li-ion diffusivityin the charging and discharging of a Li-ion battery, in order to improvethe Li-ion diffusivity and therewith the power characteristics andadditionally to increase the capacity of a Li-ion battery.

These objects are achieved by a process for the preparation of compoundsof general formula (I)

Li_(a−b)M¹ _(b)Fe_(1−c)M² _(c)P_(d−e)M³ _(e)O_(x)   (I),

wherein Fe has the oxidation state +2 and M¹, M², M³, a, b, c, d, e andx are:

-   M¹: Na, K, Rb and/or Cs,-   M²: Mn, Mg, Al, Ca, Ti, Co, Ni, Cr, V,-   M³: Si, S, F-   a: 0.8-1.9,-   b: 0-0.3,-   c: 0-0.9,-   d: 0.8-1.9,-   e: 0-0.5,-   x: 1.0-8, depending on the amount and oxidation state of Li, M¹, M²,    P, M³,    wherein compounds of general formula (I) are neutrally charged,    comprising the following steps-   (A) providing a mixture comprising at least one lithium-comprising    compound, at least one iron-comprising compound, in which iron has    the oxidation state +3, and at least one M¹-comprising compound, if    present, and/or at least one M²-comprising compound, if present,    and/or least one M³-comprising compound, if present, and at least    one reducing agent which is oxidized to at least one compound    comprising at least one phosphorous atom in oxidation state +5, and-   (B) heating the mixture obtained in step (A) at a temperature of 100    to 500° C. and at an autogeneous pressure to reduce Fe to oxidation    state +2 and to obtain a compound of general formula (I).

In a preferred embodiment, M¹, M², M³, a, b, c, d, e and x have thefollowing meanings:

-   M¹: Na,-   M²: Mn, Mg, Al, Ca, Ti, Co, Ni,-   M³: Si, S, F,-   a: 0.6-1.6, particularly preferred 0.9-1.3,-   b: 0-0.1,-   c: 0-0.6, particularly preferred 0-0.3-   d: 0.6-1.6, particularly preferred 0.9-1.3-   e: 0-0.3, particularly preferred 0-0.1-   x: 2-6, depending on the amount and oxidation state of Li, M¹, M²,    P, M³,    wherein compounds according to general formula (I) are neutrally    charged.

For example, in a very preferred embodiment, M¹, M² and M³ are absent,in order to have a neutrally charged compound of general formula (I)LiFePO₄, in which Fe is in oxidation state +2. Therefore, in a verypreferred embodiment, the process according to the present invention isconducted in order to obtain the compound of formula LiFePO₄.

In further preferred embodiments, M¹, being for example Na, is presentin an amount of up to 10 mol %, in respect of the sum of Li and M¹. Inanother preferred embodiment, M², being for example Mn, is present in anamount of up to 30 mol %, in respect of the sum of iron (II) and M²present in the compound. In another preferred embodiment, M³, being forexample Si, is present in an amount of up to 10 mol %, in respect of thesum of phosphorous and M³.

Process steps (A) and (B) are explained in the following in more detail:

Step (A):

Step (A) of the process according to the present invention comprisesproviding a mixture comprising at least one lithium-comprising compound,at least one iron-comprising compound, in which iron has the oxidationstate +3, and at least one M¹-comprising compound, if present, and/or atleast one M²-comprising compound, if present, and/or least oneM³-comprising compound, if present, and at least one reducing agentwhich is oxidized to at least one compound comprising at least onephosphorous atom in oxidation state +5.

In general, all Li-, M¹-, M²-, M³- and Fe(III)-comprising compoundsknown to a person having ordinary skill in the art which are able to beincorporated in an essentially aqueous mixture in step (A) of theprocess can be used in the process according to the present invention.

The Li-comprising compound in step (A) is preferably chosen from thegroup consisting of lithium hydroxide LiOH, lithium hydroxide-hydrateLiOH·H₂O, lithium acetate LiOAc, lithium carbonate Li₂CO₃,lithium-phosphates, -phosphites, -hypophosphites, like LiH₂PO₄, Li₂HPO₄,Li₃PO₄, LiH₂PO₃, Li₂HPO₃, and/or LiH₂PO₂, and mixtures thereof. In avery preferred embodiment, lithium hydroxide LiOH and/or lithiumhydroxide-hydrate LiOH·H₂O and/or lithium carbonate Li₂CO₃ are used aslithium-comprising compounds in step (A) of the process according to thepresent invention. Two particularly preferred lithium-comprisingcompounds are lithium hydroxide LiOH and lithium hydroxide-hydrateLiOH·H₂O.

The at least one lithium-comprising compound is added to the mixture instep (A) in the process according to the present invention in aconcentration of in general 0.04 to 3 mol Li/L, preferably 0.2 to 2.0mol Li/L, particularly preferred 0.3 to 1.5 mol Li/L, based on the wholereaction mixture in each case.

In general, all iron-comprising compounds in which iron has theoxidation state +3, known to a person having ordinary skill in the artcan be used in the process according to the present invention, which areable to be incorporated in a preferably essentially aqueous mixture instep (A) of the process. According to the present invention, a singleiron-comprising compound in which iron has the oxidation state +3, or amixture of different iron-comprising compounds in which iron has theoxidation state +3 can be used. It is also possible that aniron-comprising compound is used in which both, iron in oxidation state+2 and +3 is present, like for example Fe₃O₄. It is also possible that amixture of different iron-comprising compounds is used comprising onecompound in which iron has the oxidation state +3 and another compoundin which iron has the oxidation state +2.

In a preferred embodiment, the iron-comprising compound in which ironhas the oxidation state +3 is chosen from the group consisting of iron(II,III)-oxide, iron(III)-oxide, iron (III)-oxide hydroxide, oriron(III)-hydroxide, for example Fe₃O₄, alpha-Fe₂O₃, gamma-Fe₂O₃,alpha-FeOOH, beta-FeOOH, gamma-FeOOH and Fe(OH)₃. Preferred are thealpha-, beta- and gamma-modification of iron(III)-oxide hydroxide(FeOOH) and Fe(OH)₃.

The iron-comprising compound has in general a BET surface, measuredaccording to methods known to a person having ordinary skill in the art,of at least 5 m²/g, preferably at least 50 m²/g, more preferably atleast 150 m²/g. The BET surface is in general not larger than 1000 m²/g.If iron-comprising compounds are used having a very high BET surface,the reaction time of the process can be decreased, giving rise to aprocess according to the present invention, which is faster and moreeconomic than the processes of the prior art.

The at least one iron-comprising compound is added to the mixture instep (A) in the process according to the present invention in aconcentration of in general 0.04 to 4.0 mol Fe/L, preferably 0.1 to 2.0mol Fe/L, particularly preferred 0.2 to 1.5 mol Fe/L, based on the wholereaction mixture in each case.

The at least one M¹-comprising compound, if present, is preferablychosen from the group consisting of sodium hydroxide NaOH, sodiumacetate NaOAc, sodium carbonate Na₂CO₃, and mixtures thereof. In a verypreferred embodiment, sodium hydroxide NaOH and/or sodium carbonateNa₂CO₃ are used as sodium-comprising compounds in step (A) of theprocess according to the present invention.

The at least one M²-comprising compound, if present, is preferablychosen from compounds having the required cation and an anion chosenfrom hydroxide, acetate, oxide, carbonate, halogenide, like fluoride,chloride, bromide, iodide, nitrate, and mixtures thereof. In a verypreferred embodiment, the anion of the at least one M²-comprisingcompound is acetate, oxide, hydroxide, carbonate, nitrate, or mixturesthereof.

The at least one M³-comprising compound, if present, is preferablychosen from H₂SO₄, (NH₄)HSO₄, (NH₄)₂SO₄, LiHSO₄, Li₂SO₄, finely dividedSiO₂, e.g. in form of a sol, H₄SiO₄, Li-silicate, NH₄F, LiF, HF,polycarbon monofluoride, polycarbon fluoride, poly(carbon monofluoride),graphite fluoride, Li₂SiF₆, (NH₄)₂SiF₆and mixtures thereof.

M¹-, M²-, and/or M³-comprising compounds are added to the preferablyessentially aqueous mixture, if present, in amounts, in which they arepresent in compounds of formula (I). A person having ordinary skill inthe art knows how to calculate the required amount.

The process according to the present invention is conducted byintroducing at least one reducing agent into the mixture in step (A) ofthe process according to the present invention, which is oxidized to atleast one compound comprising at least one phosphorous atom in anoxidation state +5 during the process according to the presentinvention. The use of at least one reducing agent, which is oxidized toat least one compound comprising at least one phosphorous atom inoxidation state +5 has the advantage that the oxidation product of thisreducing agent gives rise to PO₄ ³⁻-anions, which are needed in order toobtain the PO₄ ³⁻-comprising compound of general formula (I).

In a preferred embodiment, the at least one reducing agent that isoxidized to at least one compound comprising at least one phosphorousatom in oxidation state +5, is carbon free. According to the presentinvention, carbon free means that no carbon atoms are present in thephosphorous-containing reducing agent. An advantage of a carbon freereducing agent, like H₃PO₃, is that the reduction can be conducted atlow temperatures of at most 300° C. in a hydrothermal process, whereasfor example carbon as reducing agent makes temperatures necessary of600° C. and higher. These low temperatures according to the presentinvention make it possible to obtain nano-crystalline materials.Nano-crystalline materials tend to agglomeration at high temperatureswhich are in general necessary if for example carbon is used as thereducing agent.

In a preferred embodiment, the at least one reducing agent which isoxidized to at least one compound comprising at least one phosphorousatom in an oxidation state +5 is chosen from the group consisting ofH₃PO₃, (NH₄)H₂PO₃, (NH₄)₂HPO₃, H₃PO₂, (NH₄)H₂PO₂, LiH₂PO₃, Li₂HPO₃,LiH₂PO₂ and mixtures thereof. In a particularly preferred embodimentH₃PO₃, (NH₄)H₂PO₃, (NH₄)₂HPO₃ are used, a very preferred reducing agentis H₃PO₃.

The at least one reducing agent which is oxidized to at least onecompound comprising at least one phosphorous atom in oxidation state +5is added to the mixture in step (A) in the process according to thepresent invention in a concentration of in general 0.04 to 2.0 mol P/L,preferably 0.1 to 1.3 mol P/L, particularly preferred 0.15 to 1.0 molP/L, based on the whole reaction mixture in each case.

According to the present invention at least one reducing agent which isoxidized to at least one compound comprising at least one phosphorousatom in oxidation state +5 is added to the reaction mixture in step (A)of the process according to the present invention. The reducing agentthat is used in the process according to the present invention willpreferably be oxidized to PO₄ ³⁻. If the at least one reducing agentwhich is oxidized to at least one compound comprising at least onephosphorous atom in oxidation state +5 is added to the reaction mixturein a preferably at least equimolar amount, particularly preferred in anequimolar amount, PO₄ ³⁻ is obtained as the oxidizing product in anamount high enough to be the complete amount of phosphate-anion PO₄ ³⁻of the compound of general formula (I). According to this embodiment nocompound having at least one phosphorous atom in oxidation state +5 hasto be added.

In another preferred embodiment of the present application the mixturewhich is provided in step (A) additionally comprises at least onecompound comprising at least one phosphorous atom in oxidation state +5.In this preferred embodiment of the present invention a combination ofat least one reducing agent which is oxidized to at least one compoundcomprising at least one phosphorous atom in oxidation state +5 and atleast one compound comprising at least one phosphorous atom in oxidationstate +5 is added to the reaction mixture in step (A) of the processaccording to the present invention. In this embodiment of the processaccording to the present application, PO₄ ³⁻ that is obtained as theoxidizing product does not need to be present in an amount high enoughto be the complete amount of phosphate-anion of the compound of generalformula (I), because, in this embodiment, at least one compound havingat least one phosphorous atom in oxidation stage +5 is also added. Thisat least one compound comprising at least one phosphorous atom inoxidation state +5 will be the second source of PO₄ ³⁻-anions, whichhave to be incorporated into the compound of general formula (I).

Preferred compounds comprising at least one phosphorous atom inoxidation state +5 which are optionally added in step (A) are chosenfrom the group consisting of H₃PO₄, (NH₄)H₂PO₄, (NH₄)₂HPO₄, (NH₄)₃PO₄,Li₃PO₄, LiH₂PO₄, Li₂HPO₄ and mixtures thereof. Particularly preferredare H₃PO₄, (NH₄)H₂PO₄, (NH₄)₂HPO₄ and mixtures thereof, very preferredis H₃PO₄.

The at least one compound comprising at least one phosphorous atom inoxidation state +5 is added to the mixture in step (A) in the processaccording to the present invention in a concentration of in general 0.04to 2.0 mol P/L, preferably 0.1 to 1.3 mol P/L, particularly preferred0.15 to 1.0 mol P/L, based on the whole reaction mixture in each case.

If compounds are used in the process according to the present inventionthat bear two functionalities in respect of the present process, likefor example compounds that comprise a lithium-cation and a PO₄ ³⁻- orPO₃ ³⁻-anion, the amounts of the compounds, which are introduced intothe reaction mixture, are adjusted in a way that all necessarycomponents are present in the reaction mixture in amounts that aresuitable for obtaining the compound according to general formula (I). Aperson having ordinary skill in the art does know how to calculate theseamounts.

In a further preferred embodiment, in addition to the at least onereducing agent which is oxidized to at least one compound comprising atleast one phosphorous atom in oxidation state +5 and optionally at leastone compound comprising at least one phosphorous atom in oxidation state+5, at least one additional reducing agent is added to the mixture instep (A) of the process according to the present invention. Theadditional reducing agent may also be carbon-free or may contain carbon.

The at last one additional reducing agent is preferably chosen fromhydrazine or derivatives thereof, hydroxyl amine or derivatives thereof,reducing sugars, like glucose, saccharose (succhrose) and/or lactose,alcohols like aliphatic alcohols having 1 to 10 carbon atoms, likemethanol, ethanol, propanols, for example n-propanol or isopropanol,butanols, for example n-butanol, iso-butanol, ascorbic acid, compoundscomprising easily oxidisable double bonds, and mixtures thereof.

Examples of derivatives of hydrazine are hydrazine-hydrate,hydrazine-sulfate, hydrazine-dihydrochlorid and others. An example of aderivative of hydroxyl amine is hydroxyl amine-hydrochloride.Particularly preferred carbon-free reducing agents which are notoxidized to at least one compound comprising at least one phosphorousatom in oxidation state +5 are hydrazine, hydrazine-hydrate, hydroxylamine or mixtures thereof.

The at least one reducing agent, which is optionally added in step (A)of the process according to the present invention, is on the one hand bynature not able to deliver PO₄ ³⁻-anions as oxidation products which canbe incorporated into the compound of general formula (I). On the otherhand the at least one reducing agent does not have the total reductivepotential to reduce the Fe(III) precursor completely into Fe(II).Therefore, if at least one of these additional reducing agents is used,it is also necessary to use these reducing agents in combination with atleast one compound which is oxidized to a compound comprising at leastone phosphorous atom in oxidation state and optionally at least onecompound comprising at least one phosphorous atom in oxidation state +5in order to obtain compounds of general formula (I) having theadvantageous electrochemical characteristics and microstructureaccording to the present invention. In these cases the amount and theconcentrations of the at least one compound which is oxidized to atleast one compound comprising at least one phosphorous atom in oxidationstate +5, optionally at least one compound comprising at least onephosphorous atom in oxidation state +5 and optionally at least oneadditionally reducing agent, which are added in step (A), have to beadjusted accordingly. A person having ordinary skill in the art doesknow how the respective amounts have to be calculated.

The at least one additional reducing agent is optionally added to themixture in step (A) in the process according to the present invention ina concentration which depends strongly on the reducing power andreducing potential of this agent. A person having ordinary skill in theart does know how the respective amount has to be calculated.

In general the molar ratio between the at least one reducing agent whichis oxidized to at least one compound comprising at least one phosphorousatom in oxidation state +5 and at least one compound comprising at leastone phosphorous atom in oxidation state +5 is 0.8 to 1.5, morepreferably 0.9 to 1.1, most preferably 1.0.

In another embodiment, if a combination of at least one reducing agentwhich is oxidized to a compound comprising at least one phosphorouscompound in oxidation stage +5, preferably H₃PO₃, and at least onecompound comprising at least one phosphorous atom in oxidation stage +5,preferably H₃PO₄, is added in step (A) of the process according to thepresent invention, this combination is preferably added in a ratio, forexample, H₃PO₃/H₃PO₄, which is larger than the ratio that is necessaryto obtain the desired compound according to general formula (I), toovercome oxidative influences within the synthesis route, e.g. withinthe preparation of the mixture in the presence of oxygen and/or withinthe optional calcination of the dried material in the presence of oxygenimpurities. A person having ordinary skill in the art does know how tocalculate the stoichiometric amounts of the components in the mixture ofstep (A) according to the present invention.

In a preferred embodiment, the at least one lithium-comprising compound,the at least one iron-comprising compound, in which iron has theoxidation state +3, the at least one reducing agent which is oxidized toat least one compound comprising at least one phosphorous atom inoxidation state +5, and optionally the at least one compound comprisingat least one phosphorous atom in oxidation state +5, are added to theessentially aqueous mixture in amounts that are adjusted in a way thatthe stoichiometry according to general formula (I) is obtained. A personhaving ordinary skill in the art does know how to calculate thenecessary amounts.

In another preferred embodiment of the present invention, the at leastone lithium-comprising compound is added in an amount that is ≧1% byweight, preferably ≧2% higher than the stoichiometric amount accordingto general formula (I).

In one embodiment of the process according to the present invention thecomponents which are present in the mixture that is provided in step (A)are mixed in dry state by intimately milling. A person having ordinaryskill in the art does know how this intimate milling can be obtained andwhich apparatuses like mills can be used. The milled components are thandissolved in a suitable amount of solvent, being preferably water.

In another embodiment of step (A) of the process according to thepresent invention, the components are mixed by subsequent dissolvingthem in the solvent, preferably in water.

The mixture which is provided in step (A) of the process according tothe present invention is in a preferred embodiment essentially aqueous.The wording “essentially aqueous” in this invention has the meaning thatmore than 50% by weight, preferably more than 65% by weight,particularly preferably more than 80% by weight of the solvent, which isused to provide the essentially aqueous mixture in step (A) of theprocess according to the present invention, is water.

In addition to water, further solvents that are miscible with water canbe present. Examples of these solvents are aliphatic alcohols having 1to 10 carbon atoms like methanol, ethanol, propanols, for examplen-propanol or iso-propanol, butanols, for example n-butanol,iso-butanol. According to the present invention, alcohols can be addedin step (A) of the process according to the present invention asadditional reducing agent and/or as additional solvent.

In a very preferred embodiment, the solvent that is used in step (A) ofthe process according to the present invention is water without anyadditional solvents. In the context of the present invention the wording“without any additional solvents” means that in the very preferredembodiment that water is used as sole solvent, solvents other than waterare present in the reaction mixture in an amount of less than 2% byweight, preferably less than 1% by weight, more preferably less than0.15% by weight.

The order, in which the different components are added to the solvent ormixture of solvents in step (A), is not determined. In a preferredembodiment, the lithium-comprising compound is added first to thesolvent, the iron-comprising compound, in which iron has oxidation state+3, is added as the second component. Optionally the at least onecompound having at least one phosphorous atom having the oxidation state+5, and the at least one reducing agent and optionally the at least oneadditional reducing agent, are added subsequently.

In a preferred embodiment of the present invention, the mixture obtainedfrom step (A) of the process according to the present invention is anessentially aqueous solution of at least one lithium-comprisingcompound, at least one iron-comprising compound, in which iron has theoxidation state +3, at least one reducing agent which is oxidized to atleast one compound comprising at least one phosphorous atom in oxidationstate +5, optionally in combination with at least one compoundcomprising at least one phosphorous atom in oxidation state +5.

When conducted in an essentially aqueous way, step (A) can be conductedin all suitable reactors that are known to a person skilled in the art,for example an autoclave. Step (A) can be conducted continuously ordiscontinuously.

The temperature, under which step (A) of the process according to thepresent invention is conducted in an essentially aqueous way is 10 to120° C., preferably 15 to 100° C., particularly preferably 20 to 30° C.,for example room temperature. If temperatures higher than 100° C. areused, the reaction mixture has to be present in a pressure-resistantreactor, because of the boiling point of water. To increase thehomogeneity of the mixture, mixing is conducted at elevated temperatureand optionally under the application of shearing force, for example bythe use of an ultrathurrax.

In a preferred embodiment the mixture is stirred in step (A) for a timeof 0.05 to 80 hours, particularly preferred 0.1 to 20 hours, for example0.5 to 2 hours. The pH-value of the reaction mixture that is obtained instep (A) of the process according to the present invention in generalbelow pH 7, preferably below pH 6, for example at 2.0 to 5.0.

Step (A) of the process according to the present invention can beconducted under air or under an inert atmosphere. Examples of inertgases are nitrogen, noble gases like helium or argon. In a preferredembodiment, step (A) is conducted under air or under a nitrogenatmosphere.

Reduction of most of the Fe³⁺ to Fe²⁺ is in general conducted in step(B) of the process according to the present invention. It is alsopossible that reduction immediately starts in step (A) after addition ofthe reducing agent in the aqueous mixture. In this embodiment, at leastpart of Fe(III) is reduced to Fe(II) in step (A) of the processaccording to the present invention. It is further possible thatreduction starts after the aqueous mixture is heated to an increasedtemperature of 40 to 100° C., preferably 60 to 95° C. In anotherpreferred embodiment, if a combination of two P-comprising compounds isused as the reducing agent, for example H₃PO₃/H₃PO₄, the reductionstarts, when both components are added.

Step (B):

Step (B) of the process according to the present invention comprisesheating the mixture obtained in step (A) at a temperature of 100 to 500°C. and at an autogeneous pressure to reduce Fe to oxidation state +2 andto obtain a compound of general formula (I).

Step (B) of the process according to the present invention is conductedin general at a temperature of 100 to 500° C., preferably at 180 to 400°C., most preferably at 220 to 320° C., for example at 250 to 300° C.

In one embodiment, step (B) of the process according to the presentinvention, can be conducted under hydrothermal conditions, whereinliquid water and water vapour are present in equilibrium, for example ata temperature of 100 to 374.15° C. Conducting step (B) of the processaccording to the present invention under hydrothermal conditions ispreferred. Under hydrothermal conditions autogeneous pressures of 1 barat 100° C. to 220 bar at 374° C. are present in the autoclave.

In another embodiment, step (B) of the process according to the presentinvention, is conducted under supercritical conditions, for example at atemperature of above 374.15° C. If step (B) of the process according tothe present invention is conducted under supercritical conditions, thereaction mixture is present in a supercritical phase. In thisembodiment, a pressure of 500 bar and more can be obtained, depending onthe filling degree of the autoclave.

Step (B) of the process according to the present invention is conductedin general at a pressure of 1 to 200 bar, preferably at 2 to 150 bar,most preferably at 50 bis 100 bar. The pressure which is present in step(B) of the process according to the present invention can in oneembodiment be set by the components of the reaction mixture, which isheated to the mentioned temperatures. For example, if water is thesolvent of the reaction mixture prepared in step (A) and treatedhydrothermally in step (B) of the process according to the presentinvention, it will evaporate at a temperature above 100° C. If step (B)is conducted in a sealed reactor, for example an autoclave, the pressurewill rise in this reactor caused by the evaporating solvent. In a verypreferred embodiment, step (B) of the process according to the presentinvention is conducted in an autoclave.

In a second embodiment of the process according to the presentinvention, the pressure of the reaction mixture in step (B) can beadjusted by the addition of at least one suitable gas to the reactor.This gas is preferably an inert gas, most preferably chosen from noblegases like argon, helium or mixtures, or nitrogen. In a preferredembodiment of the process according to the present invention, nitrogenis used as inert gas.

In a further embodiment of the process according to the presentinvention, the reaction mixture obtained from step (A) is placed in asuitable reactor, for example an autoclave, followed by adjusting thepressure in the reactor to a pressure above atmospheric pressure, beingfor example 1.5 to 20 bar, most preferably 5 to 15 bar, for example 10bar. Subsequently, the reaction mixture is heated to a temperature whichis desired, preferably as mentioned above, wherein the pressure rises atthe same to the values as mentioned above.

Step (B) of the process according to the present invention can beconducted in any reactor, which is suitable for the temperature andpressure of step (B). In a preferred embodiment, step (B) of the processaccording to the present invention is conducted in an autoclave. In amore preferred embodiment, step (B) of the process according to thepresent invention is conducted in the same reactor as step (A) of theprocess.

Step (B) of the process of the present invention can be conductedcontinuously or discontinuously.

Heating according to step (B) of the process according to the presentinvention is conducted as long as it is necessary to obtain a compoundaccording to formula (I). In a preferred embodiment, step (B) of theprocess according to the present invention is conducted for 0.5 to 30hours, preferably 4 to 20 hours, most preferably 8 to 16 hours, forexample 12 hours.

In general, the reaction mixture is stirred in step (B) of the processaccording to the present in invention. In a preferred embodiment, themixture is stirred in step (B) very rapidly, in order to obtaincompounds of general formula (I), which are very homogeneous. Thestirrer speed in step (B) is preferably 400 to 1200 rpm (rounds perminute), more preferably 600 to 100 rpm, for example 700 rpm. Thestirrer speed in step (B) has a significant effect on the quality of theproducts obtained from the process according to the present invention.Suitable stirrers are known to a person having ordinary skill in theart, for example blade stirrer.

After step (B) of the process according to the present invention theproduct, at least one compound according to general formula (I), mostpreferably LiFePO₄, is obtained in the solvent, which has been appliedin step (A) of the process. In a preferred embodiment of the processaccording to the present invention, water is used as the solvent. In thecase that other compounds according to general formula (I) not beingLiFePO₄ are prepared by the process according to the present invention,either solutions or emulsions are obtained in step (B) depending on thesolubility of these compounds in the solvent. In the preferred case thatLiFePO₄ is obtained in the process according to the present invention,an aqueous suspension of LiFePO₄ is obtained in step (B).

If an emulsion is obtained after step (B) of the process according tothe present invention, which is preferred, this emulsion has a pH-valueof in general 3 to 7, preferably 4.5 to 6.5, for example 5.5.

The present invention also relates to a compound according to generalformula (I) as defined above, preparable by a process according to thepresent invention.

In a preferred embodiment of the process according to the presentinvention, the reaction mixture, which is obtained from step (B) issubjected to step (C), which is an optional separating step, in order toseparate the compound according to general formula (I) from the reactionmedium.

Step C:

In a preferred embodiment of the process according to the presentinvention, after step (B), the following step (C) is conducted:

-   (C) separating the compound of general formula (I) from the mixture    obtained in step (B).

In general, all methods that are known to a person having ordinary skillin the art for separating solid materials from solution or emulsion canbe used in step (C) of the process according to the present invention.Preferred methods are filtration, centrifugation, drying. In a preferredembodiment of step (C), the at least one compound of general formula (I)which is obtained in step (B) in, preferably aqueous, emulsion isseparated in step (C) by filtration, preferably supported by applicationof increased or reduced pressure. A person having ordinary skill in theart does know how to conduct this.

In a further preferred embodiment of the process according to thepresent invention, after separation of the at least one compound ofgeneral formula (I) in solid form, this solid is washed, in order toobtain the at least one compound in essentially pure form. In respect ofthe process according to the present invention. “Essentially pure” meansthat less than 5% by weight, preferably less than 2% by weight, morepreferably less than 1% by weight compounds are present after washingthat are not compounds of general formula (I).

In a preferred embodiment, washing is conducted with a suitable solvent,in which the at least one compound of general formula (I) is essentiallyinsoluble. “Essentially insoluble” means that less than 5% by weight,preferably less than 2% by weight, more preferably less than 1% byweight of the at least one compound of general formula (I) is dissolvedduring the washing procedure.

In respect of the process according to the present invention,“essentially” means more than 90%, preferably more than 95%, morepreferably more than 98%.

In a very preferred embodiment, washing in step (C) of the processaccording to the present invention is conducted with water. In a morepreferred embodiment of the present invention, washing is conducted withseveral portions of water, instead of one complete portion of water. Ingeneral, washing is conducted as many times as necessary, in order toobtain the compound according to general formula (I) in essentially pureform. A method to determine the amount of water that is necessary toobtain an essentially pure compound is, for example, the conductivity ofthe compound, wherein an essentially pure compound shows a very lowconductivity.

In a further preferred embodiment, the at least one compound that isobtained after step (C) of the process according to the presentinvention, is dried, in order to remove the solvent, preferably water.Drying can be conducted by any method known to a person having ordinaryskill in the art, for example heating to a temperature of 40 to 150° C.In a further embodiment of the process according to the presentinvention, drying can be conducted under reduced pressure, for exampleat 400 to 900 mbar. Drying by heating can be conducted in any apparatussuitable for drying and known to the skilled artisan, for example in ahot-air cabinet or in any kind of furnaces.

Drying in step (C) of the present invention is conducted as long asessentially the whole amount of solvent, preferably water, is removed. Aperson having ordinary skill in the art does know, when essentially allsolvent is removed, for example all solvent is removed if the compoundof general formula (I) reaches a constant weight.

The solids that are obtained from step (C) of the process according tothe present invention supply improved Li-ion diffusivity in the chargingand discharging of a Li-ion battery containing them. By improving theLi-ion diffusivity the power characteristics and additionally thecapacity of a Li-ion battery can be increased.

Therefore the present invention also relates to particles oragglomerates comprising at least one compound of general formula (I)obtainable/preparable by the process according to the present invention.

Because of this fact the particles or agglomerates comprising at leastone compound according to general formula (I) preparable by the processaccording to the present invention are particularly suitable for the usefor the preparation of a cathode of a lithium-ion battery or anelectrochemical cell. Therefore the present invention also relates tothe use of compounds of general formula (I) obtainable/preparable by theprocess according to the present invention for the preparation of acathode of a lithium-ion battery or an electrochemical cell.

In addition, the present invention relates to a cathode for alithium-ion battery, comprising at least one particle or agglomeratespreparable to the process according to the present invention or at leastone compound according to general formula (I) preparable by the processaccording to the present invention.

Step (D):

In one embodiment of the process according to the present invention, thesolid compound obtained from step (C) is optionally calcinated at acalcination temperature of 300 to 1000° C. in an optional step (D) ofthe process according to the present invention.

Optional step (D) is preferably conducted at a calcination temperatureof 375 to 1100° C., particularly preferably at a calcination temperatureof 400 to 950° C., for example 450 to 850° C.

Calcination is in general conducted under an inert gas atmosphere.Examples of inert gases are nitrogen, technical nitrogen comprisingtraces of oxygen or noble gases like helium and/or argon. In a preferredembodiment, nitrogen is used in optional step (D) of the processaccording to the present invention. If technical nitrogen is used inoptional step (D) of the present invention, this nitrogen can comprisetraces of oxygen.

One advantage of the process according to the present invention is thatcalcination can be conducted under an inert atmosphere and no needexists to conduct optional step (D) under a reducing atmosphereaccording to the prior art. Based thereon the process according to thepresent invention can be conducted in a more time and cost saving way.The absence of a gaseous reducing agent, for example hydrogen, avoidsthe presence of explosive gaseous mixtures. If the nitrogen used in thecalcination step comprises higher amounts of oxygen, it is possible toadd reducing gases like CO or hydrogen to the oxygen comprisingnitrogen.

Optional step (D) of the process according to the present invention isconducted for a time of 0.1 to 8 hours, preferably 0.5 to 3 hours. In apreferred embodiment of optional step (D), the calcination temperatureis hold for a period of 0.1 to 2 hours, very preferably 0.5 to 1.5hours, and at the end the temperature is decreased to room temperature.

The temperature of calcination has a significant impact onto thespecific surface of the compound according to general formula (I). Lowtemperatures during calcination give normally rise to high specificsurface area. High temperatures during calcination give usually rise tolow specific surface area.

The particles or agglomerates that are obtained in step (D) of theprocess according to the present invention can optionally comprisefurther elements, for example carbon, that are optionally obtained bypyrrolysis of the additional reducing agent, for example, a sugar.

The process according to the present invention can be conductedcontinuously or discontinuously. In a preferred embodiment the processaccording to the present invention is conducted continuously. Suitableapparatuses for optional step (D) are known to the person havingordinary skill in the art. One example for a discontinuous or continuouscalcination is a rotary furnace. In case of continuous calcination theresidence time in a rotary furnace is based on the inclination and therotating speed of the furnace. A person having ordinary skill in the artdoes know how a suitable residence time is adjusted in the rotaryfurnace. In a preferred embodiment the solid that is calcinated in step(D) of the process according to the present invention is moved duringcalcination, for example in a fluidized bed reactor or in a rotaryfurnace. The solid can also be stirred during calcination. The rotaryfurnace can comprise different temperature zones. For example, in afirst zone the temperature is adjusted to a low temperature in order todrain the spray dried powder, whereas in another zone a highercalcination temperature is present. The speed of heating of the powderis depending on the temperatures in the different zones and on the speedwith which the powder is moved in the furnace.

Optional step (D) of the process according to the present invention isin general conducted under a pressure that is suitable that preferablycomplete conversion into the desired products is obtained. In apreferred embodiment optional step (D) is conducted under a pressurewhich is slightly higher than atmospheric pressure, in order to preventoxygen penetrating the reactor from the outside. This slightly increasedatmospheric pressure is preferably caused by at least one inert gas thatis streaming over the solid compound that is calcinated in this step.

Depending on the composition of the electrode which can be prepared formthe compound of general formula (I) and on the desired electrochemicalproperties of the resulting lithium-ion battery, it can be advantageous,according to the present application, if the solid compound obtainedfrom step (C) is mechanically treated prior to optional step (D) and/orif the solid compound obtained from step (D) is mechanically treatedafter step (D), in order to destroy the agglomerates into smaller andmore dense agglomerates having the required size or into the primaryparticles. Suitable mills, compactors and/or rolls are known to a personhaving ordinary skill in the art. Examples are jet mills which supplyvery low abrasion, preferably under the use of nitrogen and/or air. Formilling of the calcinated product also wet milling processes may beadvantageous, for example by the use of a bead mill. Further suitableapparatuses are compactors and/or rollings.

The materials according to the present invention of general formula (I)preparable by the process according to the present invention areparticularly suitable for the use for the preparation of a cathode of alithium-ion battery or an electrochemical cell. Therefore the presentinvention also relates to the use of a particle or agglomerate or ofcompound of general formula (I) obtainable/preparable by the processaccording to the present invention for the preparation of a cathode of alithium-ion battery or an electro-chemical cell.

The present invention further relates to a cathode for a lithium-ionbattery, comprising at least one particle or agglomerate compoundaccording to general formula (I) obtainable/preparable by the processaccording to the present invention. To obtain a cathode as mentionedabove the compound according to general formula (I) is mixed with atleast one electrically conducting material, described for example in WO2004/082047.

Suitable electrically conducting materials are for example carbon black,graphite, carbon fibres, carbon nanofibres, carbon nanotubes orelectrically conducting polymers. Typically 2.0 to 40% by weight of theat least one electrically conducting material are used together with thecompound according to general formula (I) in the cathode. To obtain thecathode the electrically conducting material and the compound accordingto general formula (I) are mixed, optionally in the presence of anorganic solvent and optionally in the presence of an organic binder, forexample PVDF, and this mixture is optionally formed and dried. Atemperature of 80 to 150° C. is applied in the drying step.

In a preferred embodiment at least a part of the at least oneelectrically conducting material or at least one precursor of anelectrically conducting material is added during the preparation ofcompounds according to general formula (I) as mentioned above. In apreferred embodiment, at least a part of the at least one electricallyconducting material or at least one precursor of an electricallyconducting material is added to the mixture of the starting materials inthe preparation of the compound according to general formula (I). Theremaining part of the least one electrically conducting material or atleast one precursor of an electrically conducting material, which hasnot been added during the preparation of compounds according to generalformula (I), is added after this preparation.

Therefore, the present invention also relates to a process for thepreparation of a mixture comprising at least one compound according togeneral formula (I) as defined above and at least one electricallyconducting material comprising the following steps

-   (E) providing a mixture comprising at least one electrically    conducting material or at least one precursor of an electrically    conducting material, at least one lithium-comprising compound, at    least one iron-comprising compound, in which iron has the oxidation    state +3, and at least one M¹-comprising compound, if present,    and/or at least one M²-comprising compound, if present, and/or at    least one M³-comprising compound, if present, and at least one    reducing agent which is oxidized to at least one compound comprising    at least one phosphorous atom in oxidation state +5, and-   (F) heating the mixture obtained in step (E) at a temperature of 100    to 500° C. and an autogeneous pressure to reduce Fe to oxidation    state +2 and to obtain a mixture comprising at least one compound    according to general formula (I) and at least one electrically    conducting material.

In a preferred embodiment of this process according to the presentinvention, the mixture that is provided in step (E) is essentiallyaqueous. In a further preferred embodiment the mixture which is providedin step (E) additionally comprises at least one compound comprising atleast one phosphorous atom in oxidation state +5.

The lithium-, M¹, M² and/or M³-comprising compounds, the iron-comprisingcompounds, the at least one reducing agent which is oxidized to at leastone compound comprising at least one phosphorous atom in oxidation state+5, the optionally present at least one compound comprising at least onephosphorous atom in oxidation state +5, the electrically conductivematerials, the apparatuses and the process parameters of the steps (E)and (F) correspond to the ones described above. In addition to the atleast one reducing agent which is oxidized to at least one compoundcomprising at least one phosphorous atom in oxidation state +5, theoptionally present at least one compound comprising at least onephosphorous atom in oxidation state +5, at least one additional reducingagent can be added in a preferred embodiment, as mentioned and definedabove.

In a further preferred embodiment, the at least one reducing agent whichis oxidized to at least one compound comprising at least one phosphorousatom in oxidation state +5 is chosen from the group consisting of H₃PO₃,(NH₄)H₂PO₃, (NH₄)₂HPO₃, H₃PO₂, (NH₄)H₂PO₂, LiH₂PO₃, Li₂HPO₃, LiH₂PO₂ andmixtures thereof.

In the process for the preparation of a mixture comprising at least onecompound according to general formula (I) as defined above and at leastone electrically conducting material, the electrically conductingmaterial is chosen from the group consisting of carbon black, graphite,carbon fibres, carbon nanofibres, carbon nanotubes, electricallyconducting polymers and mixtures thereof. The at least one electricallyconducting material is in general added in step (E) of the processaccording to the present invention in an amount of 0.01 to 15% byweight, preferably 0.1 to 10% by weight, more preferably 0.2 to 8% byweight, based on the whole reaction mixture present in step (E) of theprocess according to the present invention.

If carbon black, graphite or substances essentially consisting of carbonare used as electrically conducting materials in step (E), thesematerials are preferably suspended in a mixture, preferably anessentially aqueous solution or dispersion, of the other components.This can be achieved by direct addition of these electrically conductingmaterials to the, preferably aqueous, mixture of the other components.Alternatively, carbon black, graphite or substances essentiallyconsisting of carbon can be suspended in an aqueous solution of hydrogenperoxide, and this suspension can then be added to a solution ordispersion of one or more components as mentioned above. Treatment withhydrogen peroxide normally improves the wettability of carbon with waterand makes it possible to obtain carbon containing suspensions having animproved stability, i.e. having a lower tendency for demixing. Inaddition the homogenous dispersion of the electrically conductingmaterial in the mixture is improved. By further stirring and/or heatingof the aqueous suspension the excess hydrogen peroxide is decomposedinto water and oxygen in the catalytic presence of the Li-, Fe- and/orP-containing precursors.

In another embodiment, at least one surfactant can be added in step (E)of the process according to the present invention. Suitable surfactantsare for example non-ionic surfactants, preferably ethyleneoxide/propylene oxide block copolymers.

If at least one reducing agent which is oxidized to at least onecompound comprising at least one phosphorous atom in oxidation state +5,and at least one compound comprising at least one phosphorous atom inoxidation state +5 are added in step (E) of the process according to thepresent invention, the ratio between at least one reducing agent whichis oxidized to at least one compound comprising at least one phosphorousatom in oxidation state +5, and at least one compound comprising atleast one phosphorous atom in oxidation state +5 is for example 0.8 to5.0, preferably 0.9 to 4.0, more preferably 1.0.

Step (G):

In a preferred embodiment of the process according to the presentinvention, after step (F), the following step (G) is conducted:

-   (G) separating the mixture comprising at least one compound    according to general formula (I) as defined above and at least one    electrically conducting material from the mixture obtained in step    (F).

In general, all methods that are known to a person having ordinary skillin the art for separating solid materials from solution or emulsion canbe used in step (G) of the process according to the present invention.

In principle, optional step (G) of the process according to the presentinvention can be conducted according to step (C) as described above.Therefore, the details and preferred embodiments which have beenexplained in respect of step (C) are also details and preferredembodiments of step (G) with the difference that in step (G) a mixturecomprising at least one compound according to general formula (I) asdefined above and at least one electrically conducting material istreated, whereas in step (C) at least one compound according to generalformula (I) as defined above is treated.

Step (H):

In one embodiment of the process according to the present invention, thesolid compound obtained from step (G) is calcinated at a calcinationtemperature of 300 to 1000° C. in an optional step (H) of the processaccording to the present invention.

In principle, optional step (H) of the process according to the presentinvention can be conducted according to step (D) as described above.Therefore, the details and preferred embodiments which have beenexplained in respect of step (D) are also details and preferredembodiments of step (H) with the difference that in step (H) a mixturecomprising at least one compound according to general formula (I) asdefined above and at least one electrically conducting material istreated, whereas in step (D) at least one compound according to generalformula (I) as defined above is treated.

The present invention also relates to a mixture, comprising at least onecompound according to general formula (I) as defined above and at leastone electrically conducting material, preparable by a process comprisingsteps (E), (F), and optionally (G) and/or (H) as mentioned above. Incontrast to materials according to the prior art, these mixturesaccording to the present invention show an improved dispersion of the atleast one electrically conducting material within the agglomerates ofthe resulting material. This improved C-dispersion leads to a highlyelectrically conductive percolation network of carbon within the cathodematerial powder according to the present invention and in addition to animproved electrical conductivity of the layer like electrode. Themixture comprising at least one compound according to general formula(I) and at least one electrically conducting material in general has BETsurface area which is determined by the kind and the amount of theadditional carbon within the mixture and may vary from 0.1 to 500 m²/g.

Therefore, the present invention also relates to the use of a mixture asmentioned above or agglomerates comprising the mixture, comprising atleast one compound according to general formula (I) as defined above andat least one electrically conducting material for the preparation of acathode of a lithium-ion battery or an electrochemical cell.

The present invention also relates to a cathode for a lithium-ionbattery, comprising a mixture or agglomerates comprising the mixture asmentioned above.

For the preparation of a cathode using the compound according to generalformula (I) as mentioned above or a mixture comprising the compoundaccording to general formula (I) or agglomerates as mentioned above andat least one electrically conducting material as mentioned above, in apreferred embodiment the following binders are used:

Polyethyleneoxide (PEO), cellulose, polyethylene, polypropylene,polytetrafluoroethylene, polyacrylonitrile-methylmethacrylate,styrene-butadiene-copolymers,tetrafluoroethylene-hexfluoropropylene-copolymers,polyvinylidenefluoride-hexafluoropropylene-copolymers (PVdF-HFP),perfluoroalkyl-vinylether-copolymers,vinylidenefluoride-chlorotrifluoroethylene-copolymers,ethylene-chlorofluoroethylene-copolymers, ethylene-acrylicacid-copolymers (with and without sodium ions included),ethylene-methacrylic acid (with and without sodium ions included),polyimides and polyisobutene.

The binder is normally added in an amount of 1 to 10% by weight,preferably 2 to 8% by weight, particularly preferred 3 to 7% by weight,in each case based on the whole cathode material.

The process according to the present invention is further illustrated bythe following example:

EXAMPLE 1

LiOH+FeOOH+0.5 H₃PO₃+0.5H₃PO₄→LiFePO₄+2.5H₂O

14.66 g (98%, 0.6 mol, Merck) LiOH are dissolved under stirring in 1000mL of water. 34.5 g (85%, 0.3 mol, Bernd Kraft GmbH Duisburg, Germany)H₃PO₄ are added to this solution. A white precipitate occurs having a pHof 6.5. Subsequently 64.1 g Bayoxid EF300 (FeOOH, Fe-content 51.3%, 0.6mol, BET 290 m²/g) are added. Afterwards a solution of 25.05 g H₃PO₃(98%, 0.3 mol, Acros) in 320 mL is added, a pH of 2.84 is obtained.

The reaction is conducted in a 3.5 l autoclave. The pressure in theautoclave is set to 10 bar with nitrogen. The stirrer is switched onwith 700 rpm. The reaction mixture is stirred at room temperature forone hour and is then heated to 270° C. The temperature is held at 270°C. for 12 hours and is then lowered to room temperature.

The suspension obtained has a pH of 5.52 and a conductivity of 2.09 mS.

The reaction mixture is filtrated and the solid obtained is washed with1000 mL demineralized water in 5 portions. Conductivity is 26.4 μS. Thesolid is dried at 80° C. overnight in a drying furnace until has reacheda constant weight.

EXAMPLE 2

LiOH+FeOOH+0.5H₃PO₃+0.5H₃PO₄→LiFePO₄+2.5H₂O

14.66 g (98%, 0.6 mol, Merck) LiOH are dissolved under stirring in 1000mL of water. 34.5 g (85%, 0.3 mol, Bernd Kraft GmbH Duisburg, Germany)H₃PO₄ are added to this solution. A white precipitate occurs having a pHof 6.5. Subsequently 64.1 g Bayoxid EF300 (FeOOH, Fe-content 51.3%, 0.6mol, BET 290 m²/g) are added. Afterwards a solution of 25.05 g H₃PO₃(98%, 0.3 mol, Acros) in 320 mL is added, a suspension A with a pH valueof 2.84 is obtained.

3 g carbon black (Timcal Super P Li, Timcal Deutschland GmbH, D-40212Düsseldorf, Germany) are added to the water, wherein the carbon blackswims on the surface. Subsequently, 150 ml aqueous H₂O₂-solution (30%,Merck GmbH, D-64293 Darmstadt, Germany) are added drop wise understirring, wherein the carbon black disperses in water. The black,aqueous carbon black dispersion B obtained is added under stirring tothe suspension A.

The reaction is conducted in a 3.5 l autoclave. The pressure in theautoclave is set to 10 bar with nitrogen. The stirrer is switched onwith 700 rpm. The reaction mixture is stirred at room temperature forone hour and is then heated to 270° C. The temperature is held at 270°C. for 12 hours and is then lowered to room temperature.

The suspension obtained has a pH of 5.48 and a conductivity of 2.4 mS.

The reaction mixture is filtrated and the solid obtained is washed with1000 mL demineralized water in 5 portions. Conductivity is 29 μS. Thesolid is dried at 80° C. overnight in a drying furnace until has reacheda constant weight.

EXAMPLE 3

LiOH+FeOOH+0.5H₃PO₃+0.5H₃PO₄→LiFePO₄+2.5 H₂O

14.66 g (98%, 0.6 mol, Merck) LiOH are dissolved under stirring in 1000mL of water. 34.5 g (85%, 0.3 mol, Bernd Kraft GmbH Duisburg, Germany)H₃PO₄ are added to this solution. A white precipitate occurs having a pHof 6.5. Subsequently 64.1 g Bayoxid EF300 (FeOOH, Fe-content 51.3%, 0.6mol, BET 290 m²/g) are added. Afterwards a solution of 25.05 g H₃PO₃(98%, 0.3 mol, Acros) in 320 mL is added, a suspension A with a pH valueof 2.84 is obtained.

3 g carbon black (Timcal Super P Li, Timcal Deutschland GmbH, D-40212Düsseldorf, Germany) are added to the water, wherein the carbon blackswims on the surface. Subsequently, 0.3 g Pluronic 10400 (BASF SE, 67056Ludwigshafen, Germany) are added under stirring, wherein the carbonblack disperses in water. The black, aqueous carbon black dispersion Bobtained is added under stirring to the suspension A.

The reaction is conducted in a 3.5 l autoclave. The pressure in theautoclave is set to 10 bar with nitrogen. The stirrer is switched onwith 700 rpm. The reaction mixture is stirred at room temperature forone hour and is then heated to 270° C. The temperature is held at 270°C. for 12 hours and is then lowered to room temperature.

The suspension obtained has a pH of 5.9 and a conductivity of 3.9 mS.

The reaction mixture is filtrated and the solid obtained is washed with1000 mL demineralized water in 5 portions. Conductivity is 29 μS. Thesolid is dried at 80° C. overnight in a drying furnace until has reacheda constant weight.

EXAMPLE 4

LiOH+FeOOH+0.55H₃PO₃+0.45H₃PO₄→LiFePO₄+2.5H₂O

14.66 g (98%, 0.6 mol, Merck) LiOH are dissolved under stirring in 1000mL of water. 32.75 g (85%, 0.285 mol, Bernd Kraft GmbH Duisburg,Germany) H₃PO₄ are added to this solution. A white precipitate occurshaving a pH of 6.5. Subsequently 64.1 g Bayoxid EF300 (Fe-content 51.3%,0.6 mol, BET 290 m²/g) are added. Afterwards a solution of 26.30 g H3PO3(98%, 0.315 mol, Acros) in 320 mL is added, a pH of 2.68 is obtained.

The reaction is conducted in a 3.5 l autoclave. The pressure in theautoclave is set to 10 bar with nitrogen. The stirrer is switched onwith 700 rpm. The reaction mixture is stirred at room temperature forone hour and is then heated to 270° C. The temperature is held at 270°C. for 12 hours and is then lowered to room temperature.

The suspension obtained has a pH of 5.4 and a conductivity of 2.3 mS.

The reaction mixture is filtrated and the solid obtained is washed with1000 mL demineralized water in 5 portions. Conductivity is 30 μS. Thesolid is dried at 80° C. overnight in a drying furnace until has reacheda constant weight.

EXAMPLE 5

1.1LiOH+FeOOH+0.55H₃PO₃+0.45H₃PO₄→LiFePO₄+2.5H₂O

16.13 g (98%, 0.6 mol, Merck) LiOH are dissolved under stirring in 1000mL of water. 32.75 g (85%, 0.285 mol, Bernd Kraft GmbH Duisburg,Germany) H₃PO₄ are added to this solution. A white precipitate occurshaving a pH of 6.5. Subsequently 64.1 g Bayoxid EF300 (Fe-content 51.3%,0.6 mol, BET 290 m²/g) are added. Afterwards a solution of 26.30 g H₃PO₃(98%, 0.315 mol, Acros) in 320 mL is added, a pH of 2.8 is obtained.

The reaction is conducted in a 3.5 l autoclave. The pressure in theautoclave is set to 10 bar with nitrogen. The stirrer is switched onwith 700 rpm. The reaction mixture is stirred at room temperature forone hour and is then heated to 270° C. The temperature is held at 270°C. for 12 hours and is then lowered to room temperature.

The suspension obtained has a pH of 5.7 and a conductivity of 1.2 mS.

The reaction mixture is filtrated and the solid obtained is washed with1000 mL demineralized water in 5 portions. Conductivity is 30 μS. Thesolid is dried at 80° C. overnight in a drying furnace until has reacheda constant weight.

1. A process for preparing at least one compound of formula (I)Li_(a−b)M¹ _(b)Fe_(1−c)M² _(c)P_(d−e)M³ _(e)O_(x)   (I), the processcomprising (A) heating a mixture comprising: at least onelithium-comprising compound; at least one iron-comprising compound, inwhich iron has an oxidation state +3 and is selected from the groupconsisting of iron(II, III)oxide, iron(III)oxide, iron(III)-oxidehydroxide, and iron(III)hydroxide; optionally, at least oneM¹-comprising compound; optionally, at least one M²-comprising compound;optionally, at least one M³-comprising compound; and at least onereducing agent which is oxidized to at least one compound comprising atleast one phosphorous atom in oxidation state +5, at a temperature of100 to 500° C. and at an autogeneous pressure, to reduce Fe to anoxidation state +2 and to obtain the at least one compound of formula(I),Li_(a−b)M¹ _(b)Fe_(1−c)M² _(c)P_(d−e)M³ _(e)O_(x)   (I), wherein Fe hasthe oxidation state +2, M¹ is at least one selected from the groupconsisting of Na, K, Rb, and Cs, M² is Mn, Mg, Al, Ca, Ti, Co, Ni, Cr,or V, M³ is Si, S, or F a is 0.8-1.9, b is 0-0.3, c is 0-0.9, d is0.8-1.9, e is 0-0.5, x is 1.0-8, depending on an amount and oxidationstate of Li, M¹, M², P, M³, wherein compounds of formula (I) areneutrally charged.
 2. The process according to claim 1, wherein themixture is essentially aqueous.
 3. The process according to claim 1,wherein the mixture further comprises at least one second compoundcomprising at least one phosphorous atom in oxidation state +5.
 4. Theprocess according to claim 1, wherein the at least one reducing agent isselected from the group consisting of H₃PO₃, (NH₄)H₂PO₃, (NH₄)₂HPO₃,H₃PO₂, (NH₄)H₂PO₂, LiH₂PO₃, Li₂HPO₃, and Li₂PO₂.
 5. The processaccording to claim 3, wherein the at least one second compound isselected from the group consisting of H₃PO₄, (NH₄)H₂PO₄, (NH₄)₂HPO₄,(NH₄)₃PO₄, Li₃PO₄, LiH₂PO₄, and Li₂HPO₄.
 6. The process according toclaim 2, wherein the heating (A) is conducted at a temperature of 180 to350° C.
 7. The process according to claim 1, further comprising, afterthe heating (A): (B) separating the at least one compound of formula (I)from the mixture obtained in (A).
 8. The process according to claim 1,wherein the heating (A) is conducted in an autoclave.
 9. A process forpreparing a mixture comprising the at least one compound of formula (I)as defined in claim 1 and at least one electrically conducting material,the process comprising: (F) heating a mixture comprising: the at leastone electrically conducting material or at least one precursor of anelectrically conducting material; at least one lithium-comprisingcompound; at least one iron-comprising compound, in which iron has theoxidation state +3 and is selected from the group consisting of iron(II,III)oxide, iron(III)oxide, iron(III)-oxide hydroxide, andiron(III)hydroxide; optionally, at least one M¹-comprising compound;optionally, at least one M²-comprising compound; optionally, at leastone M³-comprising compound; and at least one reducing agent which isoxidized to at least one compound comprising at least one phosphorousatom in oxidation state +5, at a temperature of 100 to 500° C. and at anautogeneous pressure to reduce Fe to oxidation state +2 and to obtainthe mixture comprising the at least one compound according to formula(I).
 10. The process according to claim 9, wherein the mixture furthercomprises: at least one second compound comprising at least onephosphorous atom in oxidation state +5.
 11. The process according toclaim 9, wherein the at least one reducing agent is selected from thegroup consisting of H₃PO₃, (NH₄)H₂PO₃, (NH₄)₂HPO₃, H₃PO₂, (NH₄)H₂PO₂,LiH₂PO₃, Li₂HPO₃, and LiH₂PO₂.
 12. The process according to claim 9,wherein the at least one electrically conducting material is selectedfrom the group consisting of carbon black, graphite, a carbon fiber, acarbon nanofiber, a carbon nanotube, and an electrically conductingpolymer.
 13. The process according to claim 2, wherein the mixturefurther comprises at least one second compound comprising at least onephosphorous atom in oxidation state +5.
 14. The process according toclaim 2, wherein the at least one reducing agent is selected from thegroup consisting of H₃PO₃, (NH₄)H₂PO₃, (NH₄)₂HPO₃, H₃PO₂, (NH₄)H₂PO₂,LiH₂PO₃, Li₂HPO₃, and Li₂PO₂.
 15. The process according to claim 3,wherein the at least one reducing agent is selected from the groupconsisting of H₃PO₃, (NH₄)H₂PO₃, (NH₄)₂HPO₃, H₃PO₂, (NH₄)H₂PO₂, LiH₂PO₃,Li₂HPO₃, and Li₂PO₂.
 16. The process according to claim 3, wherein theheating (A) is conducted at a temperature of 180 to 350° C.
 17. Theprocess according to claim 4, wherein the heating (A) is conducted at atemperature of 180 to 350° C.
 18. The process according to claim 5,wherein the heating (A) is conducted at a temperature of 180 to 350° C.19. The process according to claim 2, further comprising, after theheating (A): (B) separating the at least one compound of formula (I)from the mixture obtained in (A).
 20. The process according to claim 3,further comprising, after the heating (A): (B) separating the at leastone compound of formula (I) from the mixture obtained in (A).